Corrosion has long been a problem when certain metals or alloys are used in applications in which they come into contact with an aqueous medium. For example, in heat-transfer, e.g., cooling, systems, such as those found in internal combustion engines, alcohol-based heat transfer fluids (e.g., antifreeze compositions or components) can be very corrosive to the metal surfaces of the heat-transfer, for example, cooling, systems. Compounding this problem, the corrosion is accelerated at normal engine operating conditions, for example, including elevated temperatures. Aluminum surfaces are particularly susceptible to corrosion. See, Darden et al., “Monobasic/Diacid Combination as Corrosion Inhibitors in Antifreeze Formulations,” Worldwide Trends in Engine Coolants, Cooling System Materials and Testing, SAE Int'l SP-811, Paper #900804, pp. 135-51 (1990) (“SAE SP-811”).
Corrosion inhibitors have been used to address or at least mitigate against these problems. For example, triazoles, thiazoles, borates, silicates, phosphates, benzoates, nitrates, nitrites and molybdates have been used in antifreeze formulations. See, for example, U.S. Pat. No. 4,873,011; and SAE SP-811 at pp. 135-138, 145-46. However, such corrosion inhibitors may have several problems, including high cost, and/or provide inadequate long-term protection against corrosion. See U.S. Pat. Nos. 4,946,616; 4,588,513; and SAE SP-811, pp. 137-38. Also, most of the above-noted inhibitors are metal-specific and, as such, require multi-component formulations making them more difficult and more expensive to prepare and use commercially. See Canadian Patent No. 1,142,744.
Organic acids, such as mono- and/or di-carboxylic acids, have also been used as corrosion inhibitors. For example, see U.S. Pat. No. 4,382,008 (combination of C7-C13 di-carboxylic acid and conventional corrosion inhibitors); U.S. Pat. No. 4,448,702 (di-carboxylic acids having 3 or more carbons); U.S. Pat. Nos. 4,647,392 and 4,851,145 (combination of monobasic and dibasic acids); and U.S. Pat. No. 4,946,616 (combination of C10 and C12 diacids).
Organic acid technology (OAT) coolants use one or more organic acids as the corrosion inhibitors. Such coolants protect engine surfaces through one or more different mechanisms relative to conventional coolants including inorganic inhibitors.
Previous organic acid technology coolants have a number of problems. For example, high concentrations of organic acids, for example, much higher concentrations than concentrations of inhibitors in conventional coolants, may need to be used in organic acid technology (OAT) based coolants to provide the desired degree of corrosion protection, especially for heavy duty applications. Also, one organic acid, sebacic acid, which is used in several commercial antifreeze compositions, e.g., Texaco's “Havoline” Extended Life AntiFreeze/Coolant; General Motors' “Dex-Cool” AntiFreeze/Coolant; Canadian Tire's “Motomaster” Long Life and is currently used in the standard formulation set forth by the British Military (see Specification TS 10177, “Antifreeze, Inhibited Ethanediol, AL-39”), is difficult to use commercially since it is commercially available as a solid, and requires heat to dissolve it in a heat transfer fluid. Further, sebacic acid and higher di-carboxylic acids tend to have poor solubility in antifreeze formulations, for example, using hard water. See U.S. Pat. No. 4,578,205.
In addition, certain organic acids have been shown to be aggressive towards polymeric components, such as seals, hoses, etc., of cooling systems. Such aggressiveness may result in substantial costs to repair and even replace all or part of the cooling system. Also, organic acids may cause coolant turbidity and/or instability which may create operational issues, such as the need to more frequently service the cooling system and/or replace the coolant. Such service/replacement disadvantageously increase operation costs and equipment downtime.
European Patent Publication No. 0479470A1 relates to corrosion inhibitors having at least one acid having the following general structure:
wherein the groups R1, R2 and R3 are the same or different C1-C10 alkyls, or, alternately, wherein one of R1, R2 and R3 is H, and the other two R groups are C1-C10 alkyls. However, this publication does not disclose any specific combination of mono-carboxylic acids and does not disclose, teach or suggest which combinations of acids would be useful. In fact, the only multi-acid combinations disclosed include sebacic acid, which, as previously discussed, has several disadvantages.
U.S. Pat. No. 4,851,145 discloses a corrosion inhibitor for use in aqueous and liquid alcohol compositions including combinations of an alkylbenzoic acid or salt thereof; a C8-C12 aliphatic monobasic acid or salt thereof; and a hydrocarbyl triazole. An additional, optional corrosion inhibitor in the form of a C8-C12 aliphatic dibasic acid or salt thereof may be employed.
Corrosion inhibitors containing neodecanoic acid (a mono-carboxylic organic acid) have also been suggested. U.S. Pat. No. 4,390,439 (“Schwartz et al.”) relates to the use of neodecanoic acid as a corrosion inhibitor in hydraulic fluids. However, Schwartz et al. does not disclose, teach or suggest other organic acids (except benzoic acid) used alone or in combination with neodecanoic acid as a corrosion inhibitor.
SAE SP-811 also describes neodecanoic acid as a possible corrosion inhibitor. However, SAE SP-811 relates to the use of combinations of mono-carboxylic acids and di-carboxylic acids, including sebacic acid, as corrosion inhibitors. Although SAE SP-811 suggests that neodecanoic acid is effective as a corrosion inhibitor, it states that “[t]he use of neodecanoic acid is limited by solubility considerations . . . ” (p. 147).
Thus, it would be desirable to provide new compositions useful in OAT coolants and methods for making such compositions and OAT coolants, for example, that are relatively easy, and operationally and cost effective to use and practice.